Calculators using delay line memories and serial data processing are well known in the art, as shown by U.S. Pat. No. 3,328,763 granted to H. M. Rathburn et al. While these calculators can perform some complex calculations involving more than one mathematical function or operation, several, even redundant, key strokes are usually required. For example, to multiply sine X times cosine X, the argument X must be entered into prior art calculators twice. A calculator constructed according to the present invention reduces the number of key strokes required in many calculations by including a capability to readily recall the last number (Last X) utilized in an immediately preceding calculation or the result of such a calculation if that result would be destroyed by the next calculation to be performed by the calculator.